Do Incandescent Solids Follow Stefan's Law?

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Discussion Overview

The discussion centers on whether all incandescent solids adhere to Stefan's law, specifically the fourth power law of temperature, and the implications of emissivity on this relationship. Participants explore theoretical aspects and the behavior of different materials under varying conditions.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant asserts that all incandescent solids follow the T^4 law but suggests that the constants differ among them.
  • Another participant questions the assumption that the constant remains unchanged across all temperatures, seeking clarification on the logical basis for this claim.
  • A different participant states that Stefan's constant (\sigma) is consistent across all temperatures and bodies, while the actual law involves emissivity (\epsilon), which varies.
  • It is noted that while \sigma is a universal constant, the emissivity may change with temperature, potentially complicating the application of the law.

Areas of Agreement / Disagreement

Participants express differing views on the constancy of the constants involved and the behavior of emissivity, indicating that multiple competing perspectives remain without a consensus.

Contextual Notes

The discussion highlights potential limitations regarding the assumptions about emissivity and its dependence on temperature, as well as the implications for the practical application of Stefan's law.

neelakash
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Do all incandescent solids obey the fourth power law of temperature?

I think they all obey [tex]\ T^4[/tex]
But the constants are different for them.

Agreed?
 
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Are you saying that for a particular object, the "constant" remains constant for T=0 to infinity? What logical basis have you for such a conjecture? (Of course, it may not be a conjecture, may be an actual law -- that's what we're discussing here.)
 
Stefan's constant [tex]\sigma[/tex] has the same value for all temperatures and all bodies.

But the actual law is [tex]\ I=[/tex] [tex]\epsilon[/tex][tex]\sigma[/tex][tex]\ T^4[/tex]

where [tex]\epsilon[/tex] is the emissivity.

I think [tex]\sigma[/tex] is constant for all but [tex]\epsilon[/tex] varies.
 
Last edited:
You are correct: sigma is a universal constant.

For the same body, the emissivity may vary with temperature. So, I = e*sigma*T^4 actually becomes meaningless practically if e varies too much with T for a given body.
 

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